The study of optical properties of amorphous thin films of mixed oxides In<Subscript>2</Subscript>O<Subscript>3</Subscript>—SnO<Subscript>2</Subscript> system,deposited by co-evaporation

A discussion of optical properties of mixed oxides In₂O₃—SnO₂ system is presented. Film thickness, substrate temperature, composition (in molar %) and annealing have a profound effect on the structure and optical properties of these films. Initially the increase in band gap with the increase of SnO₂ content in In₂O₃ is due to the increase in carrier density as a result of donor electrons from tin. The decrease in band gap above the critical Sn content is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The increase in band gap with film thickness is caused by the increase in free carrier density which is generated by (i) Sn atom substitution of In atom, giving out one extra electron and (ii) oxygen vacancy acting as two electrons donor. The decrease in band gap with substrate temperature and annealing is due either to the severe deficiency of oxygen, which deteriorate the film properties and reduce the mobility of the carriers, or to the formation of indium species of lower oxidation state (In²⁺).     

Approximate solution of integral equations and convolution integrals using Legendre polynomials

It has been argued that Chebyshev polynomials are ideal to use as approximating functions to obtain solutions of integral equations and convolution integrals on account of their fast convergence. Using the standard deviation as a measure of the accuracy of the approximation and the CPU time as a measure of the speed, we find that for reasonable accuracy Legendre polynomials are more efficient.     

A charge control and current-voltage model for inverted MODFET's

An analytical model is used to investigate properties of the two-dimensional electron gas (2DEG) confined in a GaAs/AlGaAs quantum well (QW) formed in a inverted modulation doped field effect transistor (MODFET). The position of the Fermi level and the average distance of the carriers in the well have been calculated as a function of the 2DEG concentration, n_s. A charge control model is presented based on the self-consistent solution of Schrodinger and Poisson's equation. The results show a unique behavior of the average distance of the 2DEG which increases with n_s, a property unique to these type of structures. The analysis is extended to model current-voltage characteristics     

Thymidine analogues for tracking DNA synthesis

Replicating cells undergo DNA synthesis in the highly regulated, S-phase of the cell cycle. Analogues of the pyrimidine deoxynucleoside thymidine may be inserted into replicating DNA, effectively tagging dividing cells allowing their characterisation. Tritiated thymidine, targeted using autoradiography was technically demanding and superseded by 5-bromo-2-deoxyuridine (BrdU) and related halogenated analogues, detected using antibodies. Their detection required the denaturation of DNA, often constraining the outcome of investigations. Despite these limitations BrdU alone has been used to target newly synthesised DNA in over 20,000 reviewed biomedical studies. A recent breakthrough in "tagging DNA synthesis" is the thymidine analogue 5-ethynyl-2'-deoxyuridine (EdU). The alkyne group in EdU is readily detected using a fluorescent azide probe and copper catalysis using 'Huisgen's reaction' (1,3-dipolar cycloaddition or 'click chemistry'). This rapid, two-step biolabelling approach allows the tagging and imaging of DNA within cells whilst preserving the structural and molecular integrity of the cells. The bio-orthogonal detection of EdU allows its application in more experimental assays than previously possible with other "unnatural bases". These include physiological, anatomical and molecular biological experimentation in multiple fields including, stem cell research, cancer biology, and parasitology. The full potential of EdU and related molecules in biomedical research remains to be explored.     

Control of chemoselectivity in Dieckmann ring closures leading to tetramic acids

An efficient strategy for the control of the chemoselectivity in Dieckmann ring closures leading to tetramic acids derived from serine and α-methyl serine is reported, and this provides pathways to diversely substituted systems from a common starting material.     

Approaching polymetallic 'assemblies of assemblies' using ligands with multiple functionality--novel Mn10M2 (M = alkali metal) chains with 'ionophoric' end cavities

A tri-functional ligand with hydrazone, oxime and o-vanillin subunits uses separate encoded coordination instructions to create a novel extended spin-coupled cluster where the hydazone oxygen and oxime groups of three ligands combine to create bridges linking ten Mn ions together, leaving organized O(6) end cavities capable of coordinating oxo-philic cations.     

Spin frustration in a Cu(II)3 triangle frustrated?

A spiral hexanuclear antiferromagnetic Cu(II) complex with a [Cu(3)(μ(2)-NO)(3)(μ(3)-O)] triangular core has direct metal spin coupling through diazine (μ(2)-NN), oxime (μ(2)-NO) and oxide/hydroxide (μ(3)-O) bridges. Spin frustration, expected in the triangular core, is suppressed (frustrated) by the bridging antiferromagnetic connections to the external metals, and so any residual spin in the triangle effectively cannot be stabilized.     

Measurement of naturally occurring/fallout radioactive elements and assessment of annual effective dose in soil samples collected from four districts of the Punjab Province,Pakistan

Soil samples were collected from different localities of districts Jhelum, Chakwal, Rawalpindi and Attock, Punjab Province, Pakistan with an aim to measure naturally occurring radionuclides, namely ²²⁶Ra, ²³²Th, ⁴⁰K and fallout ¹³⁷Cs radionuclide using a P-type coaxial high purity germanium (HPGe) γ-ray spectrometer. Measured specific activities of ²²⁶Ra, ²³²Th and ⁴⁰K in these soil samples ranged from 26.02 ± 7.11 to 93.54 ± 8.13 Bq kg⁻¹, 29.34 ± 2.58 to 114.41 ± 2.80 Bq kg⁻¹ and 348.15 ± 3.20 to 752.98 ± 4.20 Bq kg⁻¹, respectively. Activity due to ¹³⁷Cs was observed in some locations which ranged from 0.4 ± 0.2 to 7.8 ± 0.3 Bq kg⁻¹. From the measured activity concentrations, radium equivalent activity concentrations were determined followed by calculations of mean absorbed dose rate and mean annual effective dose for the inhabitants of the studied area. The mean radium equivalent activity, internal and external hazard indices values came out to be 179.26 ± 11.93 Bq kg⁻¹, 0.64 ± 0.05 and 0.48 ± 0.03, respectively. Indoors and outdoor average annual effective dose values were found to be 0.42 ± 0.03 and 0.10 ± 0.01 mSv, respectively. Present data have been compared with the published data for other parts of the world and found to be safe for public and environment.     

Structural, magnetic and electronic structure studies of Mn doped TiO2 thin films

We report structural, magnetic and electronic structure study of Mn doped TiO₂ thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO₂) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L_3,2 edge show that Mn²⁺ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L_3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO₂ films.